In the field of oil well servicing, the practice of fracturing a subterranean formation accessed by a wellbore is standard procedure. During this fracturing procedure, large amounts of abrasive fluid-solids mixtures of fracturing fluids are pumped down the wellbore to the formation by high pressure pumps. A fracturing block or frachead, capable of withstanding high pressures and resistant to erosion, is attached to a wellhead or other tubular structures fixtures located on a wellhead, and fluid lines from high pressure pumps are attached to the frachead. The frachead directs the fracturing fluid through the wellhead and down the wellbore. The interior bore of the frachead is subjected to extreme erosion from the abrasive fluid-solids mixtures. When erosion of the frachead reaches a certain point, the frachead no longer safely has the strength required to contain the pressure of the fracturing fluids and must be taken out of service and repaired if possible. Repairs by welding are time consuming and can introduce metallurgical problems, such as hardening, cracking and stress relieving, due to the welding procedure. Alternatively, it is known to fit a frachead with a replaceable abrasion resistant wear sleeve and thus minimize abrasive wear on the pressure retaining walls of the frachead. The wear resistant frachead body is coupled through a flanged connection to a lower tubular structure which may be the wellhead itself or an intermediate sub or spool structure. Both the frachead and lower tubular structure can be fit with wear sleeves.
Conventional flanged connections have a ring seal which comprises a corresponding and a circumferentially extending groove on the flange of the frachead body and a circumferentially extending groove on the flange of the spool structure. A deformable ring seal or ring gasket is sandwiched and sealably crushed between the flanges when coupled. The ring gasket is typically expected to seal on its first use, and may only successfully be reused once or twice more. The circumferentially extending grooves for the gasket seals can also deform after repeated installations of new gasket seals, and must eventually be repaired. Such deficiencies in the grooves are usually not apparent and are not noticed until the failure of the seals.
Furthermore, the radial spacing between the bore, the circumferentially extending grooves and the bolts circle of the flange are set by API (American Petroleum Institute) standards and thereby constrain the maximum bore that can extend concentrically therethrough, limiting the maximum size of any wear sleeves. Accordingly, retrofit or provision of a lower tubular member with a wear sleeve results in a smaller wear sleeve bore.
There is a need for an improved system for wear sleeves for frac head installations which maximizes the flow bore and obviates the limitations of the existing ring seals.